More checkstyle improvements on Offer components

src/main/java/de/rwu/easydrop/model/Offer.java

@@ -13,35 +13,35 @@ import lombok.Data;
 
 @Data
 public class Offer {
-    /*
-     * The product that our software buys
+    /**
+     * The product that our software buys.
      */
-    Product sourceProduct;
+    private Product sourceProduct;
 
-    /*
-     * The product that our software sells
+    /**
+     * The product that our software sells.
      */
-    Product saleProduct;
+    private Product saleProduct;
 
-    /*
-     * Date of the creation of the offer
+    /**
+     * Date of the creation of the offer.
      * NOTE: Use Timestamp? https://docs.oracle.com/javase/8/docs/api/java/sql/Timestamp.html
      */
-    Date creationDate;
+    private Date creationDate;
 
-    /*
-     * Date of last update of the offer on the destination website (API)
+    /**
+     * Date of last update of the offer on the destination website (API).
      */
-    Date upDate;
+    private Date upDate;
 
-    /*
-     * Date of last check if offer is still valid
+    /**
+     * Date of last check if offer is still valid.
      */
-    Date checkDate;
+    private Date checkDate;
 
-    /*
-     * ID of the offer
+    /**
+     * ID of the offer.
      */
-    String offerId;
+    private String offerId;
 
 }

src/main/java/de/rwu/easydrop/service/validation/OfferValidator.java

@@ -7,7 +7,7 @@ import de.rwu.easydrop.model.Offer;
  *
  * @since 0.2.0
  */
-public class OfferValidator {
+public final class OfferValidator {
         /**
      * Private constructor to prevent unwanted instantiation.
      *

src/main/java/de/rwu/easydrop/service/writer/OfferWriter.java

@@ -22,7 +22,7 @@ public class OfferWriter {
     /**
      * Validates and saves product to persistence.
      *
-     * @param product
+     * @param offer
      */
     public void writeOfferToPersistence(final Offer offer) {
         OfferValidator.validate(offer);